I've used Archival Mist for several years to deacidify the historical letters that I collect. It is easy to use and (at least in my experience) virtually fool-proof unless you really saturate the paper (which is unnecessary). However, it will obviously be many more years before anyone will be able to tell whether it really helps to preserve paper (particularly later 19th century paper that was made with acidic wood pulp). The only objection that I have is that the price seems to have really jumped over the past several years. On the other hand, none of its competitors are cheap either. The price aside, I've been quite happy with this product.